Conventionally, as disclosed in Patent Literature 1, there has been known a system capable of heating, by means of a heat pump (12), feedwater supplied to a feedwater tank (23) of a boiler (24). Further, as disclosed in Patent Literature 2, there has been also known a system (S1) that generates steam by means of a heat pump (10). The system is separated into a heating unit (21 (a first heat exchanger 40)) that heats water to the temperature near the boiling point and an evaporating unit (22 (a second heat exchanger 41)) that evaporates water.